The present invention relates to updating temperature information of an on die thermal sensor (ODTS), and more particularly, to a circuit for correctly updating temperature information regardless of an operation mode of a dynamic random access memory (DRAM).
A dynamic random access memory (DRAM) cell includes a transistor for operating as a switch and a capacitor for storing a charge, i.e., data. According to whether the capacitor stores the charge, i.e., whether a terminal voltage of the capacitor is high or low, a logic level of the data is determined as a high level or a low level.
Since the data is stored in the capacitor as an accumulated electrical charge form, there is no power consumption for the data storage ideally. However, since there occurs a leak current due to a PN junction of a metal oxide semiconductor (MOS) transistor, the stored initial charge may be discharged and, thus, the data may vanish.
To prevent data loss, the data stored in a memory cell is read and the read data is restored into the memory cell by recharging the memory cell with a normal charge before the data vanishes. This operation should be periodically performed in order to maintain data.
The above-mentioned recharging operation is called a refresh operation and, generally, a control of the refresh operation is performed by a DRAM controller. Due to the refresh operation, refresh power is consumed. In case of a battery operated system, which requires lower power consumption, reducing power consumption is very important and is a critical issue.
One method of reducing the power consumption for the refresh operation is changing a refresh period according to temperature. As the temperature decreases, a data holding time of the DRAM is longer. Therefore, by dividing a temperature range into several temperature regions and by lowering a frequency of a refresh clock at a relative low temperature region, power consumption is reduced.
Accordingly, a device for correctly sensing the temperature of the inside of the DRAM and for adjusting the refresh clock frequency is required.
As a semiconductor unit is highly integrated and is operated at a higher speed, a significant amount heat is generated. The generated heat increases internal temperature of the semiconductor unit and, thus, can prevent the semiconductor unit from normal operation. The generated heat may cause a defect in the semiconductor unit.
Therefore, a device for correctly sensing the temperature of the semiconductor unit and for outputting the sensed temperature information is needed.